Thermostatic switch



Sept. 9, 1958 F. ROSEN THERMOSTATIC SWITCH Filed March 27. 1957 INVENTORFRANK ROSEN FIG-5.

ATTORNEY THERMOS'IATIC SWITCH Frank Rosen, Pittsford, N. Y., assignor toWestinghouse Electric Qorporation, East Pittsburgh, Pin, a corporationof Pennsylvania This invention relates to a thermally responsive controldevice including a switch structure actuated by a differential expansionrod and tube type thermal sensing element and has as an object toprovide an improved control of this type constructed to occupy a minimumamount of space and in which a simple and small enclosure may beprovided for the switch or switches associated therewith.

A further object of this invention is to improve the construction of athermally responsive control switch of the above type to make it moreeasily adjustable for operation at different temperatures.

Another object of this invention is to provide an improved control inwhich a single thermally responsive actuator is used to operate aplurality of separately adjustable electric switches.

A still further object of this invention is to provide improvedconstruction for switches of the above mentioned type wherein theswitches are of the snap acting type and in which the temperaturedifferential of each switch may be easily and independently adjusted.

In accordance with this invention, a thermally responsive control may beconstructed to include one or more electric switches separately mountedon a base, the contacts of each switch being supported by resilientelements projected laterally from a column or stack mounted on the base.A switch actuating lever has one end pivotally supported on the base onone side of said columns and extends past. said columns with its otherend being located at the other side of the columns to actuate one ormore of said resilient elements. Secured to the base adjacent thepivotally supported end of the lever is a differential expansion rod andtube type thermomotive device which extends from the base on the sideopposite said switches. A portion of this thermal motive device extendsthrough the base and engages the lever causing it to actuate theswitches in response to changes in the temperature of the thermomotivedevice. If only one switch is supported on the base, the leverpreferably is formed with a hole intermediate its ends through which theswitch column extends and the lever extends closely along said basebetween it and the resilient contact supporting elements projecting fromthe column.

When a pair of switch assemblies are mounted on the base to be actuatedby the lever in accordance with this invention, the switches may bedisposed to straddle the lever in order to keep the control compact. Forthe latter arrangement, the lever may be provided with a cross bar orside projections having portions engageable with eachof the switches tobe actuated thereby. The switches are of the snap acting type and haveindependent adjustments to determine the temperature at which they areactuated and, also, the temperature differential between opening andclosing of their contacts.

In some space heating installations, a blower or fan is provided toforce air over a heat exchanger after the latter attains a predeterminedtemperature. The temperature ambient the heat exchanger will be keptwithin safe limits by a thermally responsive control which will PatentedSept. 9, 1958 ice automatically deenergize the heat source when thecontrol senses a predetermined temperature. A control having twoindependently adjustable switches and made in accordance with thisinvention is particularly useful in this type of installation where asingle thermally responsive actuator actuates one switch to turn on thefan when air ambient the heat exchanger reaches a first temperature,keeping the fan energized at all temperatures thereabove. The controlalso includes a safety or limit switch actuated by the same thermallyresponsive actuator to deenergize or shut off the heat source in theevent the temperature sensed by the actuator rises above a second highervalue.

The foregoing and other objects are effected by the invention as will beapparent from the following description and claims taken in connectionwith the accompanying drawings, forming a part of this application, inwhich:

Fig. 1 is a vertical section of a thermally responsive control deviceincluding two switches, taken just inside the cover for the switches,with one switch partially cut away to show details of its construction;

Fig. 2 is a vertical section taken on line II-II of Fig. 1;

Fig. 3 is a vertical section taken on line III-III of Fig. 1;

Fig. 4 is a front elevation of a thermally responsive switchillustrating a modification of this invention;

Fig. 5 is a side elevation of the switch of Fig. 4.

The thermally responsive control device 11, shown in Figs. 1 through 3,comprises a metal base plate 13 on which are mounted a pair of switches14 and 15. Extending between the switches, and closely straddled thereby, is a switch actuating lever 17 in the form of relatively stiff orrigid metal bar having one end pivotally supported on the base by ahinge spring 19. The other end of the actuating lever carries atransversely extending cross bar 21 engageable with the switches 14 and15 for operating them in a manner to be explained hereinafter.

Supported from the base 13 adjacent the pivoted end of the actuatinglever is a thermomotive structure comprising a thermally expansibletubular member 25 made of copper or other metal having a substantialtemperature coeflicient of linear expansion. This tubular member has oneend peened or upset to secure it in an opening 26 in the base 13 andextends therefrom on the side opposite the switches. The tubular member25 encloses a rod 2'7 for actuating the lever 17 and formed of materialhaving an extremely low temperature coeificient of linear expansion suchas a ceramic material or a metal alloy of the type well known as Invar.One end of the rod abuts an adjustable plug 29 threaded in the outer endof the tubular member 25. The other end of the rod extends through theopening 26 in the plate 13 and abuts a notch in the lever 17 adjacentthe pivoted end of the latter. The hinge spring 19 biases the lever 17into engagement with the rod.

When the tubular member 25 is heated, it expands longitudinally withrespect to the rod 27 and the force applied on the lever by the rod inopposition to the biasing force of the spring 19 is relieved. Thus, asthe tubular member 25 is heated, the lever 17 moves toward the base 13and, as the tubular member cools, the lever moves away from the base 13.

washers for insulating the arms 32 and 34 from each other,

a plate 39 which supports an adjusting screw 41 for the arm 34 andstiffening plates 44 for the arm 34 as referred to hereinafter.

The snap acting arm 34 is formed with 'a dimpled or non-developable area42 intermediate the column 35- and the' contact 33 to-provide itwith twopositions of stability on opposite sides of a critical center position.The dimpled area 42 of the spring arm has a hole 43 at its center and apair ofresilient stiffening plates 44 are clamped in the column 35 andextend therefrom along and closely adjacent to opposite sides of-thespring arm to stiffen the portion of the arm between the hole and thecolumn. These plates 44 taper to a point adjacent the hole 43 and arebiascdtowar'd an electrically insulating ceramic pin 43 in the adjustingscrew 41. The screw 41 is: threaded in a sleeve 45 fastened to the plate39 and has a manually adjustable knob 46 for adjusting the switch 14.The position-of the pin48 which engages the end of one ofthe plates 44,-determines the critical point at which the snap acting arm 34 will moveover center.

The spring arm 3-2 carrying the contact 31 is biased in the directionaway from thesna'pacting spring arm 34, but the movement of the arm 32is limited by engagement heating installation.

of its outer end with the head of a screw 47 threaded in the cross bar21 on the end of the actuating lever 17. In the stable position of thesnap acting arm 34 illustrated in Fig. 2 the contact 33 is in-engagementwith the contact 31 on the resilient arm 32. If,.in response to heatingof the tubular member, the actuating lever is shifted sufficiently tothe right, lookingvat Fig. 2,.the head of the screw 47 willpushtheresilient arm-32 and its contact 31 against the contact 33on thesnapacting arm 34 and cause the latter to snap over center to its otherposition of. stability in which the contacts will be disengaged. Afterthe snap acting arm34=is snapped over center to disengage the contacts,it may be returned to the position shown in Fig. 2 bymovement-ofthe'lever 17 to the left in response to cooling of tube 25,whereupon the cross bar 21 engages the end of the snapacting arm 34 andmoves it over center. Thescrew 47 is adjustable in the cross bar 21 tovary the distance between the screw head and the cross barand adjust thetemperature'differential between opening and closing of the contacts ofswitch 14.

Referring to Fig. 3, the structure of the switch 15 shown thereincomprises relatively movable contacts 51 and 53 supported on the endsofa snap acting arm 52 and a resilient arm 54,.respectively. These armsare supported in a column 55 in a manner similar to the assembly of Fig.2 and, like the arms of switch 14, extend generally parallel to the:actuating lever 17. However, the snap acting arm 52' and resilient arm54 have been interchanged so thatthe snap acting arm 52 is engaged bythe head ofa screw 57'threaded-in the cross bar 21 whereas the resilientarm 54" is engageable by the cross bar 21. The screw 57, like screw 47,provides an adjustment of the differential between opening and closingtemperatures for switch 15. The snap acting arm 52 also has a centralnondevelopable area 58 with a hole 59 at its center to make the arm snapacting. Clamping plates 61, similar to the plates 44 of Fig. 2, aredisposed on opposite sides of the snap acting arm 52 to stiffen itbetween the hole 59 at the center of its non-developable surface and thecolumn 55 in which the plates and one end of the snap acting arm aresecured. The plates 61 are biased towards anadjusting screw 63, threadedin a sleeve 66 mounted on a plate 64 in the column 62. A ceramic pin65in the end ofthe screw 63 engages one of the clamping plates 61 at apoint adjacent the hole 59 in the snap acting arm 52. Electricalconnections to the arms 52 and 54 may be made by the terminals 67 and68, respectively, projecting from the switch stack.

The primary difference in operation between the" switches 14 and 15 ofFig. 2 and Fig. 3 is that movement of the lever 17 due to heating of thetube 25 causes the contacts of switch 15 to close, but causes thecontacts of the switch 14 to separate.

Although the switches 14 and 15 may be adjusted to operate at anydesired temperatures, a preferred embodiment of this invention may beused in a hot air circulating As pointed out previously, the switches 14and 15 may be connected to control the heating source and fan in such aheating installation. The control device 11 may be so located that thetube 25 is heated by ambient air being heated in a heat exchanger. Whenthe temperature of this air rises to a first temperature determined byadjustment of switch 15, the latter will be actuated to its closedposition to energize a fan to circulate air through the heat exchanger.In the event that the air temperature continues to rise the tube 25 willbe heated further and actuate switch 14 to its open position todeenergize or shut off the heat source at a second higher airtemperature determined by adjustment of switch 14. The fan wouldcontinue in operation as long as the tube 25 remained above the lattertemperature. Upon cooling tube 25 in the air ambient the heat exchanger,the heat source may be reenergized and the fan deenergized atpredetermined temperatures selected by adjusting the switches 14 and 15,respectively. Referring to Figs. 4 and 5 of the drawings, there isillustrated a second embodiment of this invention incorporating only onesnap acting switch 71. The switch comprises a resilient arm 72 and asnap acting arm 73 disposed in the same relationship and functioning inthe same manner as the arms 54 and 52 of the switch in Fig. 3,respectively. The switch 71 is illustrated, however, in its closedposition that is assumed when its thermomotive actuator is heated to apredetermined temperature. Cooperating contacts 74 and 75 are carried bythe free ends of the arms 72 and 73, respectively. The switch 71includes tapered clamping or stiffening plates 76 whose ends extend to ahole at the center of a nondevelopable area of arm 73. The plates 76, aplate 77 for supporting an adjusting screw 78 and insulating washers areassembled together with arms 72 and 73 in the same columnar or stackedarrangement 79 as in Fig. 3. The clamped ends of the arms 72 and 73extend beyond the stack to form electrical terminals 72' and 73'respectively for making connections to the switch 71.

The stacked switch assembly 79 is secured to a base plate 81 which alsoserves as a support for a rod 82 and tubular member 83 of a thermomotiveactuator for a switch actuating lever 84. The rod and tube actuator anda hinge spring 85 for supporting the lever 84 are similar inconstruction and function to the corresponding structure of Figs.-lthrough 3. The lever 84 extends along the base plate 81 and has acentral opening 86 therein through which the supporting column 79 of theswitch assembly extends for supporting the latter on the base plate 81.The free end of the lever 84 extends in the same general direction fromthe column 79 as do the switch arms 72 and 73. A rigid electricallyinsulating member 87' is fastened as by riveting to the free end of thelever 84 and has a shoulder engaged by the resilient arm 72. A screw 88is threaded in the electrically insulating member 87 and has a headoverlying the end of the snap acting arm 73 to actuate the latter. Thecontacts of the switch 71 are shown closed resulting from the snapacting arm 73 being actuated to effect contact engagement by movement ofthe lever 84 toward the base plate in response to heating oftube 83.During this movement, the screw head moved the resilient arm to theright, looking at Fig. 5, and eventually moved the free end of the snapacting arm sufficiently to force it past the critical over-center position of the arm and effect contact engagement. Upon cooling, thetubular member 83 contracts and causes the rod 82 to move the lever 84to the" left, whereupon the snap acting arm 73 will snap over-center inthe opposite direction'due to'theforce exerted thereon through the .5contacts 74 and 75 by arm 72 which is pushed by the shoulder on theelectrically insulating member 87.

In both illustrated embodiments of the invention the assemblies ofswitch components and the actuating levers are very compact and, at thesame time, permit the levers to be substantially longer than the switcharms. By having the switches 14 and 15 straddle the lever 17 in Figs. 1through 3, and by providing the hole 86 for the switch stack to extendthrough the lever 84 of Figs. 4 and 5, the actuating levers and switcharms may be arranged to extend generally parallel to each other and maybe easily enclosed in a small simple housing fastened to the metalmounting plates 13 and 81, respectively.

While the invention has been shown in several forms, it will be obviousto those skilled in the art that it is not so limited, but issusceptible of various other changes and modifications without departingfrom the spirit thereof.

What is claimed is:

1, A thermally responsive control device comprising a base, a switchstructure comprising a pair of deflectible resilient arms, a pair ofcooperating contacts supported for relative movement by said arms, acolumn of supporting and electrically insulating members anchoring oneend of each of said arms in electrically insulated relationship witheach other, said arms extending outwardly from one side of said column,a lever having one end pivotally supported on said base on the otherside of said column and extending past said column with its other endbeing engageable with at least one of said arms to actuate saidcontacts, a thermally expansible member having one end secured to saidbase and its other end extending therefrom on the side remote from saidswitch structure, a rod with a low temperature coeflicient of expansionhaving one end supported by said other end of said member, said rodextending through said base adjacent the pivotal support for said lever,means for biasing said lever into engagement with said rod, said leverbeing movable with said rod in response to a change in temperature ofsaid thermally expansible member, and manually adjustable meanssupported by said column and 6 engageable with one of said arms toselect the temperature of said member at which the conducting conditionof said contacts will be changed.

2. A thermally responsive control device comprising a base, a pair ofswitch structures supported on one side of said base in spacedrelationship, each of said structures including a pair of cooperatingcontacts, a pair of resilient, electrically conducting contact carryingarms and a column of supporting and electrically insulating elementsrigidly supporting one end of each of said arms with respect to saidbase, each of said arms extending in the same direction from saidcolumns and carrying one of said contacts, a switch actuating leverextending between said columns and having a cross bar on one end thereoffor engaging and actuating one arm of each switch structure, a pair ofscrews threaded in said cross arm and engageable with the other arm ofeach of said switch structures, respectively, the other end of saidlever being pivotally secured to said base on the side of said columnsremote from said contacts, a thermally expansible member having one endsecured to said base adjacent the pivotal support of said lever andextending therefrom on the side remote from said switch structure, a rodhaving one end supported by the other end of said thermally expansiblemember, the other end of said rod abutting said lever, a hinge springfor pivotally supporting said lever on said base and biasing the leverinto engagement with said rod, said lever being movable about itspivotal support in response to the heating of said member and separatemanually adjusted means supported by said columns for adjusting one armin each of said switch structures to determine the temperature of saidmember at which each pair of contacts will be actuated.

References Cited in the file of this patent UNITED STATES PATENTS

